1. Technical Field
The present invention relates to the field of coupling systems for coaxial cabling. More specifically, the present invention relates to a coupler which provides an automatic termination impedance when a cable is not connected to the coupler.
2. Description of the Related Art
Coaxial cables are used in many applications where high frequency signals are transmitted. Coaxial cable is also ideal in applications with low noise tolerance. A coaxial cable consists of at least one central conductor surrounded by a shielding conductor or conductors. The central and shielding conductors are separated by an insulator.
One of the most widely used applications of coaxial cabling is for cable television transmission. Most cable television subscribers have several outlets at their home or business. Generally, a splitter is used to provide a link between the service connection point outside the home and the outlet. The connection between the splitter and the outlets is provided by coaxial cabling. However, many homes have more outlets than televisions, thus outlets will remain unconnected in normal use. This can create `ghosting` problems.
Ghosting occurs when there is an impedance mismatch at some point in the coaxial cable system. High frequency signals will partially reflect at the impedance mismatch. A television receiver will then receive two versions of the desired signal: one directly and one slightly delayed from the reflection. This can create a faint image of the picture that is slightly shifted on the screen from the desired program. This ghost picture is distracting and undesirable to the viewer.
Prior cabling systems use an external terminator to help prevent ghosting. The terminator provides an impedance that matches that of the coaxial cable. This minimizes reflection of the signal. However, the user must attach the terminator to each unused outlet. External terminators can become lost or misplaced, and require manual installation or removal whenever a television is connected to or disconnected from the cabling system.
Self-terminating coaxial connectors are described in Hauver (U.S. Pat. No. 4,660,921) and Stabile (U.S. Pat. No. 5,598,132). These connectors include a resistor in a special cavity in the body of the connector. A spring loaded mechanism disconnects the resistor when a cable is plugged into the connector. However, these devices occupy a large, non-standard form factor. This requires retooling and redesign for the customer to adopt the connector. Also, prior connectors require difficult manufacturing techniques that add to the expense of the device. There is a need for a self-terminating connector that is inexpensive to manufacture and conforms to existing form factors.